Fix linking issues on Windows

Relates to #10

include/cppkafka/configuration_option.h

@@ -32,13 +32,14 @@
 
 #include <string>
 #include <type_traits>
+#include "macros.h"
 
 namespace cppkafka {
 
 /**
  * Wrapper over a configuration (key, value) pair
  */
-class ConfigurationOption {
+class CPPKAFKA_API ConfigurationOption {
 public:
     /**
      * Construct using a std::string value

include/cppkafka/message_builder.h

@@ -41,7 +41,7 @@ namespace cppkafka {
  * \brief Base template class for message construction
  */
 template <typename BufferType, typename Concrete>
-class CPPKAFKA_API BasicMessageBuilder {
+class BasicMessageBuilder {
 public:
     /**
      * Construct a BasicMessageBuilder